The studies on smoking behavior examine the effects of smoking on one's ability to do cognitive and perceptual tasks. It is known that one's heart rate increases when working on cognitive tasks and decreases when engaged in perceptual tasks. It has been proposed that such changes in heart rate are causally related to the quality of one's task performance. Activation may improve performance on a cognitive task while a decrease may improve performance on a perceptual task. Since smoking increases arousal, it may enhance cognitive functioning (and also debilitate perceptual performance). This may be one reason it is so hard for people to break the smoking habit. People worked on a cognitive task (mental arithmetic) and on a perceptual task (word cancellation) for 6 minutes each while in a physiologically restful (non-smoking) state, and later just after finishing one cigarette. This was a within-S design. The order of "rest"-"arousal" was counterbalanced across Ss. Half were light smokers and half heavy smokers. The hypotheses were supported. People were more accurate on the cognitive task after smoking compared to the non-smoking "rest" condition. Conversely, people crossed out less words on the perceptual task after smoking than in the non-smoking condition. Type of smoker was not significant. A second study, similar in design, was run with new instructions for the cognitive task. Instead of stressing accuracy it emphasized speed. A third study stressed accuracy on the perceptual task. Smoking affects accuracy or speed, depending on which instruction is employed.